The present invention relates to a new and improved method of transmitting measured or measuring values in a monitoring system.
In its more specific aspects, the present invention relates to a new and improved method of transmitting measuring or measured values in a monitoring system in which measured values determined by individual measuring stations or locations which are connected in cascade to signal lines and serving for monitoring purposes are transmitted to a number of first pairs of terminals at a central signal station. At the central signal station the measured values are then linked or processed in order to obtain differentiated or distinct malfunction or alarm signals. Furthermore, upon activation or placement into operation all measuring stations are disconnected from the signal line by a voltage change. Afterwards, the measuring stations are reconnected in a timewise staggered fashion to the signal line by means of switching elements present at each measuring station in such a manner that each measuring station additionally reconnects the next following measuring station to the line voltage after a predetermined time-delay.
To solve a multiplicity of monitoring tasks measuring stations are distributed throughout expansive structures or objects and are connected to a central signal station via a signal line. In this connection it becomes increasingly important to exactly know the origin of the measured or measuring data in order to satisfy the requirements of intelligent signal processing.
In principle, identification of the measuring stations or locations can be obtained in three different ways. The oldest known method which, however, presently finds very little use, consists of stringing individual lines from each measuring station to the central signal station. However, this solution requires an extremely high installational expense. More modern systems make use of the principle of a cascade connection in which the measuring stations are series connected and the identification is obtained by counting corresponding stepping pulses (see FIG. 1). Alternatively, fixedly addressed individual measuring stations are used which are connected in parallel to the line (see FIG. 2). A known method based on the cascade or tandem connection principle as shown in FIG. 1 is described in German Pat. No. 2,533,382, published Oct. 21, 1976. The essential difference between the two last mentioned methods is that according to the cascade connection principle all measuring stations may be identical, whereas in the system with parallel arrangement the measuring stations differ by virtue of their address and they are distinguished either by means of switches or other programming aids or accessories. It will be clear that from the view point of mass production as well as servicing and maintenance identical measuring stations have decisive advantages, and additionally, preclude the danger of any mix-up and faulty addressing. On the other hand, the fixedly impressed address affords a greater operational integrity as concerns the correct identification of the measuring stations. The known methods for identifying measuring stations in transmission systems have the following disadvantages:
(1) higher installational expense, PA0 (2) uncertainty in the identification of the measuring stations in the case of cascade connections, and PA0 (3) different measuring stations in a system with parallel connection.